Cassius believes that Brutus and he deserve just as much power as Caesar, so he does not want Brutus to be supporting Caesar, but going against him. Even though Cassius says he is equal to Caesar, he then tells Brutus a story about how he saves Caesar from almost drowning and also recalls a story of Caesar in Spain saying Alas, it cried, give me some drink, Titinius, as a sick girl (I. ii. 139). The connotation of girl is a female child, not manly and powerful.
So by telling the stories, Brutus now acknowledges that Caesar is weak because he is able to drown and get sick and Brutus will no longer look upon someone who cries as a sick girl. Brutus is persuaded by Cassius story that Caesar is not all that power and that they should not be serve Caesar as if he is a god. On the other hand, Cassius contradicts himself multiple ways by saying Caesar is like a Colossus and we petty men walk under his huge legs and peep about to find ourselves dishonorable graves.
Men at some time are masters of their fates. (I. ii. 137). Cassius portrays Caesar as a power person who will become a tyrant and that he is more superior to everyone else. Because Cassius and Brutus does not like tyrants or dictators, Cassius indirectly tells him to not support Caesar, and instead, tries hinting to Brutus that it is time for him to take control of Rome. The logos Cassius uses persuades Brutus to not let someone who is equal to him, such as Julius Caesar, to rule Rome.